1. Technical Field
The present invention relates generally to ion implanters, and more particularly, to an ion implanter system, method and program product including particle detection.
2. Related Art
Particle detection is used extensively with vacuum processes used in such industries as semiconductor fabrication. In these industries, the smallest of particles can result in substantial numbers of defective products. One particular type of device that uses a vacuum during one stage of semiconductor fabrication is an ion implanter. Ion implanters are conventionally used to alter the characteristics of a silicon wafer by injecting a layer of ions into the wafer. This process is referred to as ion implantation or doping, and the implanted ions are referred to as the dopant
Referring to FIG. 1, a conventional ion implanter 10, such as a Varian Semiconductor Equipment Associates ion implanter, is shown. Ion implanter 10 includes four general parts: a source 12, a focus line 14, an implant chamber 16 and an implant controller 17. Each part, excepting implant controller 17, is exposed to a vacuum. Source 12 receives a gas from a dopant source 18. Ions are formed into a rough beam 20 using a potential difference to pull positively charged ions into an ion analyzer 22. Ion analyzer 22 uses magnetic forces to select ions having a preferred size and potential. In particular, ion analyzer 22 conventionally forces all ions to be shifted a distance depending on their size and potential. Those that have the preferred size and potential are allowed to pass to a high voltage section 24, which controls their speed. Focus line 14 focuses the ion beam using, for example, quadrapole lenses 26, 28. Focused ion beam 30 is then moved vertically up-down and horizontally back-forth via a beam control hardware 32. Ions impact a silicon wafer(s) 34 positioned on a platen 36 in implant chamber 16. Platen 36 position may be controlled by a platen drive assembly 38 under control of a platen drive control 40. Each part of ion implanter 10 is controlled by implant controller 17.
Improved mechanical designs for ion implanters have dramatically reduced the number of particles formed by non-ion beam parameters such as friction between moving parts of platen drive assembly 38, built-up gas deposits on an interior implant chamber 16, broken wafers, etc. However, particles generated and transported by the wide aspect ratio ion beam remain a challenge. These particles may be generated, for example, by an arc occurring in ion implanter 10, ion beam 30 hitting an interior of implant chamber 16 during tuning, and a variety of other situations. Historically, few particle sensors have been implemented to detect particles in an ion beam and none have been implemented in such a way to allow control of ion implantation.
A number of approaches have been implemented to detect particles in semiconductor processing equipment in general. One approach to detect particle levels is to use a laser particle sensor. Laser particle sensors used relative to ion implanters have been limited to “dark-field” or scan laser sensors. In the dark-field approach, a laser is transmitted through an area where particles are expected to a black body dump that absorbs all of the energy. Simultaneously, photodetectors or photocells are placed off-axis (usually 90°) near the laser beam to sense reflected light from particles. The term “dark-field” is used since the laser beam is not projected on the photodetector, i.e., it is not received by the photodetector. This approach has a number of drawbacks. Foremost of these drawbacks is that a dark-field laser is incapable of looking through an ion beam, i.e., it is not transmitted through and then received by a photodetector, and is incapable of use in the presence of a bright ion beam or plasma. Dark-field lasers are also very sensitive to noise or background light, which results in particle count errors. In addition, dark-field lasers are incapable of being placed in close proximity to a wafer because debris coats the photodetector, which results in unacceptable signal degradation. To address this problem, the device is normally distanced from the wafer. This, however, results in inaccurate particle detection. Another shortcoming of conventional laser particle detectors is that they are used only during venting or vacuum pumping, and provide no information during actual ion implantation.
Another particle detection approach is disclosed in Borden et al., U.S. Pat. No. 5,606,418. In this approach, a “bright-field” laser is used to detect particles in vacuum process equipment used in processing semiconductor wafers. The term “bright-field” indicates that the laser is configured to transmit a laser beam through a very bright environment to a receiver. Particles are sensed by their breaking the path of the laser beam and the resulting amount of remittance received by the photodetector receiver. This approach, however, has never been applied to ion implanters.
One approach to particle detection that has been applied to ion implanters is disclosed in Stack, U.S. Pat. No. 5,146,098. In this approach, light generated during wafer processing is spectrally decomposed to detect characteristics of contaminating particles such as abnormal wavelength, frequency and/or energy intensity. This approach, however, does not address particles within the ion beam, but only particles within the implant chamber. In addition, Stack monitors ion implantation but does not address adjustment of the ion implantation.
In view of the foregoing, there is a need in the art for an ion implanter system having a way to detect a particle level in an ion beam and control ion implantation based on the detected particle level.